The present invention relates to a process for the production of a semiconductor laser with a tape or ribbon geometry, as well as to a laser obtained by this process. It is used in optical telecommunications.
The technical field of the invention is that of semiconductor lasers having a so-called double heterostructure. Such a structure is constituted by a stack of semiconductor layers deposited by epitaxy on a monocrystalline substrate. In general, starting from the substrate, there is a first confinement layer, an active layer (which is responsible for the light emission), a second confinement layer, a contact layer and finally a metal layer. The double heterostructure character results from the fact that the active layer is surrounded by two layers, whose composition differs from that of the active layer.
For lasers emitting between 0.8 and 0.9 .mu.m, the confinement layers are of alloy Ga.sub.1-x Al.sub.x As and the active layer and substrate are of GaAs. For lasers emitting between 1.3 and 1.65 .mu.m, the confinement layers are of Ga.sub.1-x In.sub.x As.sub.1-y P.sub.y, whilst the active layer and substrate are of InP.
The threshold current density is approximately 1 kA/cm.sup.2 for such structures. In order to reduce the threshold current, use is made of different methods making it possible to define an active, narrow tape. The latter makes it possible to confine the charge carriers and direct them towards the active zone.
Three methods are essentially known for forming said tape;
1. The implantation of protons on either side of a window, which makes it possible to produce two highly resistive regions. The current only passes into the non-implanted window. This method is e.g. described in the article by L. A. D'Asaro, published in "Journal of Luminescence", 7,310, 1973 and in the article by H. Kan, H. Namizaki, M. Ishii and A. Ito published in Appl. Phys. Lett., 27,138, 1975.
2. The diffusion of zinc up to the active zone through a silica window, whereby the diffused zone has a higher conduction than the bordering regions. This method is e.g. described in the article by H. Yonezu, I. Sakuma, K. Kobayashi, T. Kamejima, M. Ueno and Y. Nannichi, published in Jpn. J. Appl. Phys. 12, 1585, 1973 and in the article by H. Yonezu, Y. Matsumoto, T. Shinohara, I. Sakuma, T. Suzudi, K. Kobayashi, R. Lang, Y. Nannichi and I. Hayashi, published in Jpn. N. Appl. Phys., 16 209, 1977.
3. By producing a buried tape, in the manner described in the article of T. Tsukada published in "Jour. Appl. Phys.", 45, 4899, 1974.
Although satisfactory in certain respects, these three methods suffer from the following disadvantages:
The first, which has recourse to a lateral implantation of protons, does not improve the conduction in the carrier injection zone.
The second, which involves central diffusion, does not reduce the conduction in the lateral zones.
Finally, the third, uses very complex technology with in particular a repeat of the epitaxy.